'MODE_COPY_SECTION_SOURCE': undeclared identifier in copy_effects.cpp when build the project

### Tested versions

Current master

### System information

Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3060 (NVIDIA; 31.0.15.3619) - 11th Gen Intel(R) Core(TM) i7-11700K @ 3.60GHz (16 Threads)

### Issue description

When build the project, I got `MODE_COPY_SECTION_SOURCE : undeclared identifier in drivers\gles3\effects\copy_effects.cpp`


It looks like in certain cases the `copy.glsl.gen.h` did not generate the definition for `MODE_COPY_SECTION_SOURCE`

```
enum Uniforms {
COPY_SECTION,
SOURCE_SECTION,
COLOR_IN,
PIXEL_SIZE,
};

enum ShaderVariant {
MODE_DEFAULT,
MODE_COPY_SECTION,
MODE_GAUSSIAN_BLUR,
MODE_MIPMAP,
MODE_SIMPLE_COLOR,
MODE_CUBE_TO_OCTAHEDRAL,
};
```

Is there any way to debug this?

### Steps to reproduce

Not sure how I get there, but **I checked out to an old branch and rebased it to master** before I encountered this error. Maybe there is some unsync problem here? Also I can make sure that I did not have any local git changes in my repo.

### Minimal reproduction project (MRP)

N/A

Start with drivers/gles3/effects/copy_effects.cpp and the generated copy.glsl.gen.h mentioned in the report. Reproduce the build after checking out and rebasing the branch, then inspect why MODE_COPY_SECTION_SOURCE is missing from the generated header. Done means the header contains the required definition and the project builds successfully.

Written by the indexing model from the issue text.